Certain automotive vehicles are presently equipped with yaw rate sensors fixed to the structure of the vehicle for sensing rotation of the vehicle about the yaw axis. The yaw rate is combined with other information to determine, for example, that the vehicle is sliding on the road. These systems sense when the vehicle is not pointing in the direction it is moving and assist the driver in restoring correct vehicle orientation by such means as selectively activating wheel brakes.
There are many ways that knowledge that a vehicle is about to roll over or has rolled over may be applied. Examples are that preventive action can be taken, fuel delivery can be stopped, electricity to any location where it might start a fire can be turned off and automatic attempts to summon help can be initiated.
Yaw rate sensing is presently accomplished by gyroscopic devices. These may comprise such as rapidly rotating wheels driven by an electric motor, rotating light beams, or vibrating elements such as the tines of a tuning fork. Yaw rate is determined from a vibrating element by measuring forces resulting from the Coriolis Effect which is the underlying basis for the Focault Pendulum.
Current production yaw rate sensors for automobiles are based on the Coriolis effect and are able to sense yaw rates under one degree per second. Measuring Coriolis forces is technically challenging. Currently available designs are considered expensive in spite of considerable efforts to reduce their cost.
It is well known to support a flywheel by magnetic force to achieve substantially zero friction as the flywheel rotates. Many designs exist for supporting rotating flywheels with approximately zero energy loss in the bearings.
Very low coefficients of friction are achieved by coatings comprising diamond like carbon. It has been reported that friction coefficients as low as 0.001 are achieved by these coatings in a dry nitrogen environment. This is similar to and possibly less than the rolling friction encountered by a steel ball bearing ball rolling on a smooth hard surface. Such very low bearing frictions and air viscosity operate to stop rotation of a wheel relative to its housing after a period of time.
Many known sensors can measure the rate and direction of rotation of a disk. Certain of these sensors apply little or no force to the disk as the rotation is sensed. This is commonly accomplished by optical sensors responsive to a pattern in the disk and by magnetic field sensors responsive to a magnetic field that rotates with the disk. Other sensors also measure rate and direction of rotation.
CMOS active pixel image sensors are integrated circuits similar to the integrated circuits used for many years for computer memories. CMOS image sensors are made in large numbers for sensing optical images in electronic digital cameras. CMOS image sensors comprise arrays of light sensing cells and may contain more than a million cells on a single piece of silicone. Sensors having tens of thousands of cells are available at low cost. CMOS active pixel image sensors have the advantage of including both light sensing cells and logic for processing the resulting digital images on a single piece of silicone. This enables a low cost sensor to record and analyze digital images and report the results of the analysis.
Low cost CMOS active pixel image sensors have the further advantage that the small number of cells can be read quickly which enables a sensor incorporating a CMOS active pixel image sensor to analyze images and report results at a high repetition rate such as one thousand readouts and analyses per second. The high rate enables unambiguous motion detection.
Motion sensors responsive to movement of features of a digital image are well known. An example is optical “mice” used for operator input to computers which are available from several suppliers.
A general object of this invention is to provide a yaw rate or roll rate sensor for a vehicle which also overcomes certain disadvantages of the prior art.